1. Field of the Invention
The invention relates to a wireless communication device, more specifically, to a wireless communication device capable of switching antennas according to data transmission information on a network.
2. Description of the Prior Art
In modern life, people want access to useful information regardless of time or place. A wireless communication device does not require optical fibers or cable to transmit signals; therefore, it is an attractive way to exchange information. As technology progresses, portable wireless communication devices, such as cell phones and PDAs, have become important information-exchanging tools due to their convenience and portability.
As the wireless communication technology progresses rapidly, access points (AP) are widely used in today's life. Each computer in a wireless local area network (WLAN) requires a WLAN card to transmit electromagnetic signals. The AP are capable of utilizing their antennas to receive electromagnetic signals transmitted by the WLAN station. As well the AP bridges the WLAN to the Ethernet network so that information in the network is integrated and shared. Today, in order to broaden the WLAN communication distance, many AP are positioned in the coverage range of the network or they are arranged flexibly. The corresponding building method is to utilize normal Ethernet switches and CAT-5 cables to build distributed wireless AP arrangements.
Please refer to FIG. 1, which is a diagram of a network topology utilizing an access point 50 in a space. The access point 50 comprises a radiator 52 for receiving or emitting electromagnetic signals, and the coverage range of access point 50 is shown by the dotted lines shown in FIG. 1. When three users have to utilize the access point 50 to bridge the Ethernet network in the coverage range, the users share the data transmission bandwidth of the access point 50. For example, if the maximum bandwidth of the access point 50 is 11 Mbps, each user ideally gets 11/3 Mbps of the wireless data transmission bandwidth.
In the prior art, in order to raise the bandwidth or to broaden the coverage range, more AP 50 are positioned in the space. Please refer to FIG. 2, which is a diagram of a network topology utilizing three access points in a space. If three AP 50 are turned on simultaneously, the bandwidth is ideally 3 times to the bandwidth of using only one access point 50. In other words, if the maximum bandwidth of one access point is 11 Mbps, then three AP 50 ideally provide 11*3=33 Mbps bandwidth. Therefore, if three users utilize three AP 50 to bridge the Ethernet network, then each user is ideally capable of getting 33/3=11 Mbps.
As mentioned above, wireless data transmission bandwidth on the network can be raised by adding the number of AP 50. However a problem arises when a number of the AP 50 are added. If different AP use the same channel or adjacent channels, the main lobe of the transmission channel is overlapped by the side lobe of the adjacent channel such that interference occurs. Therefore, in FIG. 2, if three access points 50 are utilized simultaneously, under the 802.11b standard, the three AP 50 are capable of utilizing channel 1, channel 6, and channel 11 to transfer the wireless information for reduced the interference. Please refer to FIG. 3, which is a distributed diagram of transmission channels in the frequency domain of the 802.11b standard. In the frequency band 2.400 GHz-2.484 GHz, the peak of the main lobe of channel 1 falls on 2.412 GHz, the peak of the main lobe of the channel 6 falls on 2.437 GHz, and the peak of the main lobe of the channel 6 falls on 2.437 GHz. Therefore, between consecutive channels peaks there is about 25 MHz of bandwidth. In the actual implementation, in order to avoid the main lobe overlapping the side lobe, every two channels used have an interval of 5 channels.
As mentioned above, if the number of the AP 50 in a space is too many, interference occurs such that the transmission quality becomes lower. Further, the distance between two AP is limited and can not be too small, otherwise the combined coverage range of the AP is reduced. Thus making it more difficult to reach the users, and causing interference such that transmission dead angle occurs. In additional, each access point needs to be connected to the LAN through network lines, therefore, utilizing a number of AP increases the difficulty of wiring and building.
Furthermore, when utilizing normal AP, the radiation pattern of the prior art antenna cannot change according to different service demands, such as changes of coverage range or directivity. This makes the design of an antenna arrangement relatively inflexible and permanent.